1. Field of the Invention
The present invention relates to a nitride-based group 3–5 compound semiconductor, more particularly, to a nitride-based group 3–5 compound semiconductor represented by the general formula InxGayAlzN (wherein, x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1.
2. Description of the Related Art
As the material of light emitting diodes such as an ultraviolet or blue light emitting diode or blue laser diode and the like, group 3–5 compound semiconductors represented by the general formula InxGayAlzN (wherein, x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1) are known. Hereinafter, x, y and z in this general formula are described as InN mixed crystal ratio, GaN mixed crystal ratio and AlN mixed crystal ratio, respectively, in some cases. Of these group 3–5 compound semiconductors, particularly those containing InN in an amount of 10% or more in terms of mixed crystal ratio are particularly important for display use since light emitting wavelength in the visible region can be controlled depending on InN mixed crystal ratio.
In semiconductor light emitting diodes, a light emitting layer may be formed of multiple layers. Unless the layers have the same structure, the light emitting spectrum is an overlap of different spectrums of the layers and resultantly broadens totally. Namely, the color purity of the emitted light decreases. On the other hand, when a single light emitting layer is used, such a problem can be avoided. Further, in the case of application to a laser, when a light emitting layer is composed of a plurality of layers, the whole film thickness of the light emitting layer increases, consequently also leading to an increase in the absorption of light by the light emitting layer itself. Therefore, the minimum current required for laser oscillation can be decreased by a single layer structure of the light emitting layer.
On the other hand, in nitride-based compound semiconductors, a crystal having sufficiently high quality and large area as to enable use in crystal growth is not obtained. Therefore, growth on different substrates, so-called hetero-epitaxial growth is generally conducted. Namely, using substrates having relatively near lattice constants such as sapphire, SiC and the like, an amorphous or fine crystalline thin film called a buffer layer is first grown, and a crystal of this compound semiconductor is grown on this. However, it is common that very high density dislocation of about 108 cm−2 is present also on the thus obtained crystal. Because of such a reason, it is very difficult to form a thin film having high uniformity from this compound semiconductor, leading to difficulty in realizing high light emitting efficiency by a single light emitting layer. Consequently, under current conditions, light emitting efficiency is enhanced by using a so-called multiple quantum well using multiple light emitting layers laminated in light emitting diodes using nitride-based compound semiconductors.
An object of the present invention is to provide a single quantum well and a light emitting diode obtained by using this by a nitride-based group 3–5 compound semiconductor having high crystallinity and high quality.